what is 'artifacting'

I hear people describe one of the affects of a bad video card is artifacting. Can someone explain to me what this means?

 

artifacting is when little pixels or lines of pixels dont show up like they normally should... for example... if you had a black background as your desktop and oced your video too far you might see yellow or blue pixels scattered across the screen this basically is telling you that you went too far on your oc